Sputtering, alternatively called physical vapor deposition (PVD), is the most prevalent method of depositing layers of metals and related materials in the fabrication of semiconductor integrated circuits. Sputtering is now being applied to the fabrication of flat panel displays (FPDs) based upon thin film transistors (TFTs). FPDs are typically fabricated on thin rectangular sheets of glass. A layer of silicon is deposited on the glass panel and silicon transistors are formed in and around the silicon layer by techniques well known in the fabrication of electronic integrated circuits. The electronic circuitry formed on the glass panel is used to drive optical circuitry, such as liquid crystal displays (LCDs), organic LEDs (OLEDs), or plasma displays subsequently mounted on or formed in the glass panel. Yet other types of flat panel displays are based upon organic light emitting diodes (OLEDs).
Size constitutes one of the most apparent differences between electronic integrated circuits and flat panel displays and in the two sets of equipment used to fabricate them. Demaray et al. disclose many of the distinctive features of flat panel sputtering apparatus in U.S. Pat. No. 6,199,259, incorporated herein by reference. That equipment was originally designed for panels having a size of approximately 400 mm×600 mm. Because of the increasing sizes of flat panel displays being produced and the economy of scale realized when multiple displays are fabricated on a single glass panel and thereafter diced, the size of the panels has been continually increasing. Flat panel fabrication equipment is commercially available for sputtering onto substrates having a minimum size of 1.8 m and equipment is being contemplated for panels having sizes of 2 m×2 m and even larger, that is, substrates having an area of 40,000 cm2 or larger.
For many reasons, the target for flat panel sputtering is usually formed of a sputtering layer of the target material bonded to a target backing plate, typically formed of titanium. The conventional method of bonding a target layer to a backing plate applies a bonding layer of indium to one of the two sheet-like members and presses them together at a temperature above indium's melting point of 156° C. A more recently developed method of bonding uses a conductive elastomer or other organic adhesive that can be applied at much lower temperature and typically cured at an elevated but relatively low temperature. Such elastomeric bonding services are available from Thermal Conductive Bonding, Inc. of San Jose, Calif. Demaray et al. in the aforecited patent disclose autoclave bonding.